Contact lenses are worn on the cornea of the eye to improve sight. Both hard and soft contact lenses require periodic cleaning and disinfecting to remove protein deposits and undesirable microbes from the surface of the lens. In most cases, the lens is removed from the eye and cleaned with a lens cleaning solution. Then, the lens is disinfected. After disinfection, the lens usually is rinsed with saline solution for placement into the eye.
In the disinfecting of contact lenses, it is very important to select compositions that are effective to disinfect the lens but are not toxic to the eye. Thousands of compositions exist which are capable of disinfecting, but which exhibit toxic or undesirable discomfort to the eye when such compositions are used on lenses. Lens users sometimes fail to rinse the disinfectant solution from their lenses before placing lenses back into the eye. In some cases, lens wearers rinse their lenses poorly. Sometimes, the disinfecting composition adheres or adsorbs into the lens itself, such that even after a rinse, the relatively toxic substances from the disinfectant solution still may be temporarily retained within the surface of the lens. When that occurs, the toxic substances may be released into the eye once the lens is re-inserted. For these reasons, a desirable disinfectant solution preferably does not contain any compositions in concentration levels that exceed toxicity limits for the eye.
Unfortunately, many ophthalmic and lens care products which are effective disinfectants cause undesirable eye irritation. Also, many antimicrobial agents have a relatively narrow spectrum, and may be effective against certain microbes such as bacteria, but not against others such as fungi. Other compositions may be effective against a wide range of bacteria, yeast, and fungi, but may have limited efficacy. Many compositions that would otherwise be good lens disinfectant compositions undesirably react with other components in the lens care solution, producing unwanted side reactions and undesirable reaction products.
Magnesium perphthalate has been used in various medical applications, including contact lens disinfecting solutions. Magnesium perphthalate is a peroxy compound, and is known to have antimicrobial activity against bacteria and yeast.
Great Britain Patent 2,178,189A discloses the use of a monoperoxyphthalate salt such as magnesium monoperoxyphthalate hexahydrate in a contact lens cleaning solution. The patent teaches using magnesium monoperoxyphthalate hexahydrate in an amount from 1% to 20% by weight in aqueous solution. Another patent publication (WO 87/01562) discloses using alkaline earth metal salts of monoperphthalic acid for contact lens maintenance in aqueous concentration ranges between 0.5% and 10.0% by weight.
It recently has been discovered, however, that using such compounds in concentration ranges of 0.5% and above may have substantially adverse toxic effects to the user. Significantly elevated toxicity levels are experienced using lens care solutions having magnesium perphthalate concentrations of 0.5% or greater.
Recent data indicates that using such compounds in concentration levels below 0.5% provide surprisingly and unexpectedly reduced levels of toxicity, while still providing good lens disinfection.